U.S. patent application number 10/505958 was filed with the patent office on 2005-10-13 for microwave band radio transmission device, microwave band radio reception device, and microwave band radio communication system.
This patent application is currently assigned to Sharp Kabushiki Kaisha. Invention is credited to Suematsu, Eiji, Twynam, John Kevin.
Application Number | 20050227638 10/505958 |
Document ID | / |
Family ID | 27764388 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050227638 |
Kind Code |
A1 |
Suematsu, Eiji ; et
al. |
October 13, 2005 |
Microwave band radio transmission device, microwave band radio
reception device, and microwave band radio communication system
Abstract
An input modulation signal wave 108a is frequency-upconverted to
an intermediate frequency signal wave by a frequency mixer 3. By
adding a reference signal wave to the intermediate frequency signal
wave frequency-upconverted by the frequency mixer 3 by means of a
signal combiner 5a, an intermediate frequency multiplex signal wave
7 is generated. The intermediate frequency multiplex signal wave 7
is frequency-upconverted to a milliwave by a second frequency mixer
8. The multiplex signal wave in the milliwave band
frequency-upconverted by the second frequency mixer 8 is amplified
by a transmission amplifier 10 and transmitted as a radio multiplex
signal wave 115 constituted of a radio reference signal wave 106
and a radio signal wave 107 from a transmission antenna 15. With
this arrangement, there are provided a microwave band radio
transmitter, a microwave band radio receiver and a microwave band
radio communication system, which are excellent in controllability
of a signal level of a transmission output and able to extend a
radio transmission band and a radio transmission distance.
Inventors: |
Suematsu, Eiji; (Nara,
JP) ; Twynam, John Kevin; (Nara, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Sharp Kabushiki Kaisha
22-22, Nagaike-cho, Abeno-ku Osaka-shi
Osaka
JP
545-8522
|
Family ID: |
27764388 |
Appl. No.: |
10/505958 |
Filed: |
August 27, 2004 |
PCT Filed: |
February 25, 2003 |
PCT NO: |
PCT/JP03/02016 |
Current U.S.
Class: |
455/118 ;
455/93 |
Current CPC
Class: |
H04B 1/40 20130101; H04B
1/28 20130101 |
Class at
Publication: |
455/118 ;
455/093 |
International
Class: |
H04B 001/02; H04B
001/04; H01Q 011/12 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2002 |
JP |
2002-054272 |
Claims
1. A microwave band radio transmitter comprising: a multiplex wave
generating means generating an intermediate frequency multiplex
signal wave by adding a reference signal wave whose level is
controlled by a level control means to an input modulation signal
wave or an intermediate frequency signal wave; a second frequency
converting means frequency-upconverting the intermediate frequency
multiplex signal wave generated by the multiplex wave generating
means to a microwave; and transmission means amplifying a multiplex
signal wave of a microwave band frequency-upconverted by the second
frequency converting means and transmitting the amplified multiplex
signal wave as a radio multiplex signal wave comprised of a radio
reference signal wave and a radio signal wave.
2. The microwave band radio transmitter as claimed in claim 1,
wherein the reference signal wave is a sine wave.
3. The microwave band radio transmitter as claimed in claim 1,
comprising: a first frequency converting means
frequency-upconverting the input modulation signal wave to an
intermediate frequency signal wave.
4. The microwave band radio transmitter as claimed in claim 3,
wherein the reference signal wave is a local oscillation wave used
for the first frequency converting means.
5. The microwave band radio transmitter as claimed in claim 1,
further comprising a local oscillator for supplying a local
oscillation wave to the second frequency converting means, wherein
the local oscillator is comprised of a frequency multiplier whose
input frequency is a frequency of the reference signal wave.
6. The microwave band radio transmitter as claimed in claim 1,
wherein the second frequency converting means is a harmonic
mixer.
7. The microwave band radio transmitter as claimed in claim 1,
wherein the second frequency converting means is an even harmonic
mixer.
8. The microwave band radio transmitter as claimed in claim 1,
comprising two systems of microwave band transmission means having
the multiplex wave generating means, the second frequency
converting means and the transmission means, wherein a first input
modulation signal is inputted to one of the microwave band
transmission means, a second input modulation signal is inputted to
the other of the microwave band transmission means, and a first
radio multiplex signal wave and a second radio multiplex signal
wave, both of which are generated by the respective microwave band
transmission means, are transmitted in the forms of different
polarized waves.
9. The microwave band radio transmitter as claimed in claim 1,
wherein the radio reference signal wave in the radio multiplex wave
signal is transmitted at a power level higher than that of the
radio signal wave.
10. A microwave band radio receiver comprising a frequency
converting means frequency-downconverting a radio multiplex signal
wave transmitted from a transmission side by a radio reference
signal wave contained in the radio multiplex signal wave.
11. The microwave band radio receiver as claimed in claim 10,
comprising a variable gain amplifier for reception amplifying the
radio multiplex signal wave, wherein an intermediate frequency
signal wave is generated by frequency-downconverting the radio
multiplex signal wave amplified by the variable gain amplifier for
reception by the frequency converting means, and a gain of the
variable gain amplifier for reception is controlled by an output
signal level of the intermediate frequency signal wave.
12. The microwave band radio receiver as claimed in claim 10,
wherein the frequency converting means is a frequency mixer that
employs a microwave transistor.
13. The microwave band radio receiver as claimed in claim 12,
wherein the frequency mixer is a frequency downconverter, which has
an input terminal and an output terminal and has a short-circuit
circuit to be short-circuited at a frequency of the radio multiplex
signal wave or an intermediate frequency multiplex signal wave and
connected to an output part of the microwave transistor to which
the radio multiplex signal wave or the intermediate frequency
multiplex signal wave is inputted.
14. The microwave band radio receiver as claimed in claim 13,
wherein the microwave transistor of the frequency mixer is a
heterojunction type bipolar transistor.
15. The microwave band radio receiver as claimed in claim 10,
comprising two systems of microwave band radio receivers that have
the frequency converting means, wherein an intermediate frequency
signal is generated by frequency-downconverting two radio multiplex
signal waves transmitted in the forms of different polarized waves
from a transmission side by the two microwave band receiving means,
respectively.
16. A microwave band radio receiver comprising: a first frequency
converting means frequency-downconverting a radio multiplex signal
wave transmitted from a transmission side to an intermediate
frequency multiplex signal wave by means of a local oscillator on a
reception side; and a second frequency converting means generating
an intermediate frequency signal wave by frequency-downconverting
by means of a reference signal wave contained in the intermediate
frequency multiplex signal wave the intermediate frequency
multiplex signal wave that has been frequency-downconverted by the
first frequency converting means.
17. The microwave band radio receiver as claimed in claim 16,
wherein the second frequency converting means is a frequency mixer
that has an input terminal and an output terminal and has a
microwave transistor.
18. A microwave band radio communication system comprising the
microwave band radio transmitter claimed in claim 1 and a microwave
band radio receiver comprising a frequency converting means
frequency-downconverting a radio multiplex signal wave transmitted
from a transmission side by a radio reference signal wave contained
in the radio multiplex signal wave.
19. A microwave band radio communication system comprising the
microwave band radio transmitter claimed in claim 1 and a microwave
band radio receiver a first frequency converting means
frequency-downconverting a radio multiplex signal wave transmitted
from a transmission side to an intermediate frequency multiplex
signal wave by means of a local oscillator on a reception side; and
a second frequency converting means generating an intermediate
frequency signal wave by frequency-downconverting by means of a
reference signal wave contained in the intermediate frequency
multiplex signal wave the intermediate frequency multiplex signal
wave that has been frequency-downconverted by the first frequency
converting means.
20. The microwave band radio communication system as claimed in
claim 18, wherein the input modulation signal wave of the microwave
band radio transmitter is a signal wave comprised of either one or
a combination of two or more of a ground wave TV broadcasting wave
signal, a satellite broadcasting intermediate frequency signal wave
and a cable TV signal wave.
21. The microwave band radio communication system as claimed in
claim 19, wherein the input modulation signal wave of the microwave
band radio transmitter is a signal wave comprised of either one or
a combination of two or more of a ground wave TV broadcasting wave
signal, a satellite broadcasting intermediate frequency signal wave
and a cable TV signal wave.
Description
TECHNICAL FIELD
[0001] The present invention relates to a microwave band radio
transmitter, a microwave band radio receiver and a microwave band
radio communication system.
BACKGROUND ART
[0002] Conventionally, there has been a microwave band radio
communication system described in JP 2001-53640 A. As shown in FIG.
12, this microwave band radio communication system includes a
microwave band radio transmitter and a microwave band radio
receiver. In this case, the microwave band herein refers to a
frequency band that includes a milliwave band.
[0003] In the above-mentioned microwave band radio transmitter, an
intermediate frequency signal wave 108a (frequency: fIF) modulated
by an IF (Intermediate Frequency) modulation signal source 100 is
generated, a local oscillation wave 106b (frequency: fLo) is
generated by a milliwave band local oscillator 105, and the local
oscillation wave 106b (frequency: fLo) is frequency-upconverted by
a frequency converter 1001. The thus frequency-upconverted radio
signal wave 107 (frequency: fRF) is extracted by a bandpass filter
102 of the milliwave band and the extracted radio signal wave 107
is multiplexed with the local oscillation wave 106b by a signal
combiner 114. The local oscillation wave 106b (frequency: fLo) and
the radio signal wave 107 are amplified to appropriate levels by a
transmission amplifier 103 and radiated from a transmission antenna
15.
[0004] Then, the microwave band radio receiver on the reception
side receives the radio signal wave 107 and the local oscillation
wave 106b by a reception antenna 20, amplifies the waves to
appropriate levels by a low-noise reception amplifier 111, extracts
the radio signal wave 107 and the local oscillation wave 106b,
which are the desired waves, by the bandpass filter 102 of the
milliwave band and thereafter inputs the resulting waves to a
frequency mixer 110. The radio signal wave 107 and the local
oscillation wave 106b are subjected to square-law detection by the
square-law detection characteristic possessed by the frequency
mixer 110 to generate an intermediate frequency signal wave 108b,
and the generated intermediate frequency signal wave 108b is
inputted to a demodulator and tuner 113.
[0005] The aforementioned microwave band radio communication system
has the following problems.
[0006] (1) It is difficult to control the output levels of the
local oscillation wave (frequency fLO), the radio signal wave
(frequency fRF) and the unnecessary one-side sideband signal wave
on the transmission side.
[0007] (2) The radio transmission bandwidth is narrowed.
[0008] (3) Because of the square-law device used during the
frequency downconversion on the reception side, the detection level
in the frequency-downconverted intermediate frequency band (IF
band) is small, and it is difficult to secure a sufficient
transmission distance.
[0009] With regard to the aforementioned problem (1), the local
oscillation wave 106b used for frequency-upconverting the
intermediate frequency signal wave 108a to the radio signal wave
107 is directly added by the signal combiner 114, and a radio
multiplex signal wave 115 that is the transmission wave of the
radio signal wave 107 and the local oscillation wave 106b is
generated. In this case, if the frequency fRF of the radio signal
wave 107 and the frequency fIF of the intermediate frequency signal
wave 108a are determined, then the relation of the local
oscillation frequency fLO is uniquely determined. It is difficult
to arbitrarily set the radio signal wave 107. (frequency: fRF) in
the radio frequency band because of a problem concerning the
Wireless Telegraphy Act, and the IF frequency band of the
intermediate frequency signal wave 108a has already been a
determined frequency with regard to, for example, the TV signal
frequency and so on. Therefore, a frequency range of about 0.1 GHz
to 2 GHz is normally used.
[0010] FIG. 13 shows the relation of the frequency spectrum in the
microwave band radio communication system. As shown in FIG. 13, if
the radio frequency fRF and the intermediate frequency fIF are
fixed, then the local oscillation frequency fLO cannot be freely
set because of the radio frequency fRF (=fLO+fIF or fLO-fIf) and
the intermediate frequency fIF. Moreover, the local oscillation
wave 106b (frequency: fLO) also becomes a transmission signal, and
therefore, the local oscillation wave 106b (frequency: fLO) is also
required to have a level accurately controlled concurrently with
the radio signal wave 107 (frequency: fRF). Furthermore, when a
sideband signal wave (e.g., upper sideband) of the radio multiplex
signal wave 115 is normally used as the radio signal wave 107
(frequency: fRF), the lower sideband fLO-fIF component becomes an
unnecessary signal wave, and this signal wave is required to be
suppressed by the bandpass filter 102.
[0011] However, when the intermediate frequency signal wave 108a
(frequency: fIF) has a frequency in the UHF band (e.g., fIF=0.5 GHz
to 1.0 GHz), assuming that the frequency of the radio signal wave
is in the milliwave band (e.g., fRF=59.5 GHz to 60.0 GHz), then the
fLO+fIF component, the fLO component and the fLO-fIF component
become 59.5 GHz to 60.0 GHz, 59 GHz and 58.0 GHz to 58.5 GHz,
respectively, as shown in FIG. 13. Consequently, the intervals
between the frequencies disadvantageously come close to one
another, and it is difficult to suppress the fLO-fIF signal of the
lower sideband signal that is the unnecessary signal wave by the
normal milliwave-band bandpass filter (plane circuit filter and
waveguide filter). Furthermore, the local oscillation wave 106b
(frequency: fLO) also comes to have a frequency of 59 GHz, and it
is required to directly accurately generate a high frequency.
[0012] Furthermore, with regard to the aforementioned problem (2),
the frequency relation between the local oscillation wave 106b
(frequency: fLO) and the radio signal wave 107 (frequency: fRF) is
uniquely determined as described hereinbefore. For example, if the
frequency fIF=0.5 GHz to 1.5 GHz and fRF=59.5 GHz to 60.5 GHz, then
fLO disadvantageously becomes 59.0 GHz. Since the frequency
interval between the local oscillation wave 106b (frequency: fLO)
and the radio signal wave 107 (frequency: fRF) has a small range of
500 MHz to 1500 MHz, the second, third, . . . components of the
intermediate frequency are disadvantageously outputted in the
passband simultaneously with the frequency upconversion to the
milliwave band due to the influence of the nonlinearity of the
frequency upconverter 1001. In this case, the second harmonic wave
becomes 60.0 GHz to 62.0 GHz and outputted in the passband,
disadvantageously narrowing the radio transmission bandwidth.
[0013] Furthermore, with regard to the aforementioned problem (3),
the square-law device is employed in the reception side frequency
mixer 110 during the frequency downconversion on the reception
side, and therefore, the detection level in the
frequency-downconverted intermediate frequency band (IF band) is
small. If the reception level from the reception antenna 20 is
reduced by 6 dB, then the detection level of the intermediate
frequency signal wave 108a after the frequency downconversion is
reduced by 12 dB in terms of the relation between them. Therefore,
the detection level in the intermediate frequency band (IF band)
tends to fall into the noise band as the radio transmission
distance is extended, and it is difficult to sufficiently secure
the radio transmission distance.
DISCLOSURE OF THE INVENTION
[0014] Accordingly, the object of this invention is to provide a
microwave band radio transmitter, a microwave band radio receiver
and a microwave band radio communication system capable of
accurately controlling the levels of a radio signal wave to be
transmitted, a local oscillation signal wave to be transmitted and
an unnecessary suppression signal wave and increasing the radio
transmission bandwidth and the transmission distance.
[0015] In order to achieve the aforementioned object, a microwave
band radio transmitter of this invention comprises:
[0016] a multiplex wave generating means generating an intermediate
frequency multiplex signal wave by adding a reference signal wave
(e.g. a sine wave) whose level is controlled by a level control
means to an input modulation signal wave or an intermediate
frequency signal wave;
[0017] a second frequency converting means frequency-upconverting
the intermediate frequency multiplex signal wave generated by the
multiplex wave generating means to a microwave; and
[0018] transmission means amplifying a multiplex signal wave of a
microwave band frequency-upconverted by the second frequency
converting means and transmitting the amplified multiplex signal
wave as a radio multiplex signal wave comprised of a radio
reference signal wave and a radio signal wave.
[0019] According to the microwave band radio transmitter of the
above-mentioned construction, the intermediate frequency multiplex
signal wave is generated by adding the reference signal wave whose
level is controlled by the level control means to the input
modulation signal wave or the intermediate frequency signal wave by
the multiplex wave generating means. In this case, the
frequency-converted input modulation signal wave component, the
local oscillation wave component and the reference signal wave
component exist in the intermediate frequency multiplex signal
wave. Subsequently, the intermediate frequency multiplex signal
wave is frequency-upconverted by the second frequency converting
means. Then, the frequency-upconverted multiplex signal wave is
transmitted as a radio multiplex signal wave by the transmission
means. This radio multiplex signal wave is constituted of the
desired radio signal wave component and the desired radio reference
signal wave component. The desired radio signal wave and radio
reference signal wave can be thus separated from the unnecessary
second local oscillation wave component and the unnecessary image
signal wave component with regard to the frequency interval through
the two-time frequency conversion, and the unnecessary component
can be suppressed and filtered by the bandpass filter of the
milliwave band. Moreover, the intermediate frequency signal wave
and the reference signal wave inputted to the second frequency
converting means can easily be subjected to level control frequency
multiplex signal wave is generated by adding the reference signal
wave to the input modulation signal wave or the intermediate
frequency signal wave by the multiplex wave generating means. In
this case, the frequency-converted input modulation signal wave
component, the local oscillation wave component and the reference
signal wave component exist in the intermediate frequency multiplex
signal wave. Subsequently, the intermediate frequency multiplex
signal wave is frequency-upconverted by the second frequency
converting means. Then, the frequency-upconverted multiplex signal
wave is transmitted as a radio multiplex signal wave by the
transmission means. This radio multiplex signal wave is constituted
of the desired radio signal wave component and the desired radio
reference signal wave component. The desired radio signal wave and
radio reference signal wave can be thus separated from the
unnecessary second local oscillation wave component and the
unnecessary image signal wave component with regard to the
frequency interval through the two-time frequency conversion, and
the unnecessary component can be suppressed and filtered by the
bandpass filter of the milliwave band. Moreover, the intermediate
frequency signal wave and the reference signal wave inputted to the
second frequency converting means can easily be subjected to level
control in the stage of the intermediate frequency of a low
frequency by an AGC (Automatic Gain Control) amplifier or the like.
This also makes it possible to easily control the output levels of
the radio signal wave and the radio reference signal wave after the
second frequency conversion. Therefore, the levels of the
transmitted radio signal wave, the local oscillation signal wave
and the unnecessary suppression signal wave can be accurately
controlled, and the radio transmission bandwidth and the
transmission distance can be extended. Moreover, when the
transmission bandwidth of the intermediate frequency signal wave in
the second frequency converting means is further extended, the
transmission bandwidth can be extended in frequency by arranging a
plurality of first frequency converting means.
[0020] Moreover, in one embodiment, the reference signal wave is a
sine wave.
[0021] Moreover, a microwave band radio transmitter of one
embodiment comprises a first frequency converting means
frequency-upconverting the input modulation signal wave to an
intermediate frequency signal wave.
[0022] Moreover, in one embodiment, the reference signal wave is a
local oscillation wave used for the first frequency converting
means.
[0023] According to the microwave band radio transmitter of the
above-mentioned embodiment, by using the local oscillation wave
used for the first frequency converting means for the reference
signal wave, there is no need to employ separate oscillation
sources, and the circuit construction can be simplified.
[0024] Moreover, a microwave band radio transmitter of one
embodiment further comprises a local oscillator for supplying a
local oscillation wave to the second frequency converting means,
wherein
[0025] the local oscillator is comprised of a frequency multiplier
whose input frequency is a frequency of the reference signal
wave.
[0026] According to the microwave band radio transmitter of the
above-mentioned embodiment, by employing the frequency multiplier
as a local oscillator that supplies the local oscillation wave to
the second frequency converting section, a reference signal wave of
a stabilized frequency can be used, and stable operation can be
achieved with a simple construction obviating the need for an
independent oscillation source of a high frequency for the second
frequency converting section.
[0027] Moreover, in one embodiment, the second frequency converting
means is a harmonic mixer.
[0028] According to the microwave band radio transmitter of the
above-mentioned embodiment, the local oscillation wave is not
directly used as a transmission wave in the second frequency
converting means, and therefore, a harmonic mixer can also be
utilized. Therefore, the circuit construction and high frequency
mounting are rendered remarkably easy, and this assures a
lower-cost construction.
[0029] Moreover, by carrying out frequency conversion by the first
frequency converting means, the interval between the frequency fLO2
of the local oscillation wave and the frequency fRF
(=fLO1'fLO2+fIF1) of the radio signal wave becomes widened to
fLO1+fIF1 (=fIF2). Therefore, with regard to the influence of the
nonlinearity of the second frequency converting means on the second
intermediate frequency signal wave (frequency: fIF2=fIf1+fLO1) that
is the input signal to the second frequency converting means and
the reference signal wave (frequency: fLO1), the frequency interval
is widened in the milliwave band frequency-upconverted by the
second frequency converting means, and the unnecessary signal wave
component can easily be suppressed by the bandpass filter. As a
result, the radio transmission bandwidth can be extended.
[0030] Moreover, in one embodiment, the second frequency converting
means is an even harmonic mixer.
[0031] According to the microwave band radio transmitter of the
above-mentioned embodiment, by employing the even harmonic mixer of
an anti-parallel type diode pair and so on for the second frequency
converting means, the second harmonic component can be suppressed
and removed through the frequency-upconverting operation into the
milliwave band. Consequently, the unnecessary signal wave component
is not outputted, allowing an accurate transmission and the radio
transmission bandwidth can be more extended.
[0032] Moreover, a microwave band radio transmitter of one
embodiment comprises two systems of microwave band transmission
means having the multiplex wave generating means, the second
frequency converting means and the transmission means, wherein
[0033] a first input modulation signal is inputted to one of the
microwave band transmission means,
[0034] a second input modulation signal is inputted to the other of
the microwave band transmission means, and
[0035] a first radio multiplex signal wave and a second radio
multiplex signal wave, both of which are generated by the
respective microwave band transmission means, are transmitted in
the forms of different polarized waves.
[0036] According to the microwave band radio transmitter of the
above-mentioned embodiment, by transmitting the first radio
multiplex signal wave in the form of a vertically polarized wave,
transmitting the second radio multiplex signal wave in the form of
a horizontally polarized wave and receiving the first radio
multiplex signal wave and the second radio multiplex signal wave in
the forms of the vertically polarized wave and the horizontally
polarized wave, respectively, on the reception side, the
transmission bandwidth can be extended.
[0037] Moreover, in one embodiment, the radio reference signal wave
in the radio multiplex wave signal is transmitted at a power level
higher than that of the radio signal wave.
[0038] According to the above-mentioned embodiment, by transmitting
the radio reference signal wave in the radio multiplex signal wave
at a level higher than that of the radio signal wave, the linear
operation region of the frequency mixer on the reception side can
be extended. That is, the radio signal wave is normally a
multi-channel modulation signal wave, and the total power level of
the radio signal wave of a bandwidth wider than that of the radio
reference signal wave is large in comparison therewith. Therefore,
by making the radio reference signal wave have a level higher than
the total power of the radio signal wave and operating the
frequency mixer on the reception side with a large signal by the
radio reference signal wave, the linear detection operation region
of the frequency mixer on the reception side can be extended.
[0039] Moreover, a microwave band radio receiver of this invention
comprises a frequency converting means frequency-downconverting a
radio multiplex signal wave transmitted from a transmission side by
a radio reference signal wave contained in the radio multiplex
signal wave.
[0040] According to the microwave band radio receiver of the
above-mentioned embodiment, the intermediate frequency signal wave
is generated by frequency-downconverting the radio multiplex signal
wave transmitted from the transmission side by the radio reference
signal wave contained in the radio multiplex wave signal. In this
case, by controlling the gain at the time of amplifying the radio
multiplex signal wave by the output signal level of the
frequency-converted intermediate frequency signal wave, the
transmission distance can be extended. That is, the linear
detection operation is carried out in the region where the
transmission distance is short and the reception level is very
large, while the square-law detection operation is carried out in
the region where the transmission distance is long and the
reception level is small.
[0041] Moreover, a microwave band radio receiver of one embodiment
comprises a variable gain amplifier for reception amplifying the
radio multiplex signal wave, wherein
[0042] an intermediate frequency signal wave is generated by
frequency-downconverting the radio multiplex signal wave amplified
by the variable gain amplifier for reception by the frequency
converting means, and a gain of the variable gain amplifier for
reception is controlled by an output signal level of the
intermediate frequency signal wave.
[0043] According to the microwave band radio receiver of the
above-mentioned embodiment, by increasing the gain of the variable
gain amplifier for reception when the reception level is small, the
level inputted to the frequency mixer is increased, and the linear
detection operation region is extended. When the reception level is
too large, the gain of the variable gain amplifier for reception is
reduced, and the input level to the frequency mixer is reduced. By
doing so, a stable reception level can be obtained by reducing the
nonlinear distortion caused in the large signal region of the
frequency mixer and the amplifier, and the transmission distance
can be extended.
[0044] Moreover, in a microwave band radio receiver of one
embodiment, the frequency converting means is a frequency mixer
that employs a microwave transistor.
[0045] According to the above-mentioned embodiment, by employing
the frequency mixer that employs a microwave transistor for the
frequency converting means and providing the frequency mixer by a
two-terminal mixer that has two terminals of the input terminal and
the output terminal, there is no need to provide a circuit for
separating the radio frequency from the local oscillation frequency
at the input port dissimilarly to the normal three-terminal type
frequency mixer. In particular, the performance of the microwave
transistor type frequency mixer, which has a low conversion loss,
can be further improved.
[0046] Moreover, in a microwave band radio receiver of one
embodiment, the frequency mixer is a frequency downconverter, which
has an input terminal and an output terminal and has a
short-circuit circuit to be short-circuited at a frequency of the
radio multiplex signal wave or an intermediate frequency multiplex
signal wave and connected to an output part of the microwave
transistor to which the radio multiplex signal wave or the
intermediate frequency multiplex signal wave is inputted.
[0047] According to the microwave band radio receiver of the
above-mentioned construction, by providing the frequency mixer by
the two-terminal mixer that has two terminals of the input terminal
and the output terminal, there is no need to provide a circuit for
separating the radio frequency from the local oscillation frequency
at the input port dissimilarly to the normal three-terminal type
frequency mixer. In particular, the performance of the microwave
transistor type frequency mixer, which has a low conversion loss,
can be further improved. Furthermore, by providing a short-circuit
circuit (e.g., short-circuit stub), which is short-circuited at the
radio multiplex wave signal frequency, at the output section of the
microwave transistor to which the radio frequency multiplex wave is
inputted and making the radio multiplex signal wave reflect to and
fed back to the output terminal of the microwave transistor, the
transistor operation shifts to larger signal operation, and the
linear detection operation region is extended, allowing the radio
transmission distance to be extended.
[0048] Moreover, in a microwave band radio receiver of one
embodiment, the microwave transistor (HBT) of the frequency mixer
is a heterojunction type bipolar transistor.
[0049] According to the above-mentioned embodiment, by employing a
heterojunction type bipolar transistor for the microwave transistor
of the frequency mixer, the linear operation region can be
extended. This is because the internal operation of the transistor
tends to easily enter the large signal operation region due to
large mutual conductance possessed by the heterojunction type
bipolar transistor in comparison with FET (Field Effect Transistor)
or the like, and the linear detection operation region can be
consequently extended.
[0050] Moreover, a microwave band radio receiver of one embodiment
comprises two systems of microwave band radio receivers that have
the frequency converting means, wherein
[0051] an intermediate frequency signal is generated by
frequency-downconverting two radio multiplex signal waves
transmitted in the forms of different polarized waves from a
transmission side by the two microwave band receiving means,
respectively.
[0052] According to the above-mentioned embodiment, by
frequency-downconverting the two radio multiplex signal waves
transmitted from the transmission side with mutually different
polarized waves by the frequency converting means of the two
systems, respectively, the frequency range of the transmission band
can be extended, and a great amount of information can be
transmitted.
[0053] Moreover, a microwave band radio receiver of this invention
comprises a first frequency converting means
frequency-downconverting a radio multiplex signal wave transmitted
from a transmission side to an intermediate frequency multiplex
signal wave by means of a local oscillator on a reception side;
and
[0054] a second frequency converting means generating an
intermediate frequency signal wave by frequency-downconverting by
means of a reference signal wave contained in the intermediate
frequency multiplex signal wave the intermediate frequency
multiplex signal wave that has been frequency-downconverted by the
first frequency converting means.
[0055] According to the microwave band radio receiver of the
above-mentioned construction, the radio multiplex signal wave
transmitted from the transmission side is frequency-downconverted
to the first intermediate frequency multiplex signal wave by the
first frequency converting means by using the local oscillator on
the reception side. Then, the second intermediate frequency signal
is generated (input signal on the transmission side is reproduced)
by frequency-downconverting the intermediate frequency multiplex
signal wave by the second frequency converting means by using the
reference signal wave contained in the intermediate frequency
multiplex signal wave frequency-downconverted by the first
frequency converting means. By thus carrying out the linear
detection operation through the first frequency conversion by using
the independent local oscillator, the frequency conversion loss of
the receiver can be reduced, and the radio transmission distance
can be extended by the linear detection operation.
[0056] Moreover, in one embodiment, the second frequency converting
means is a frequency mixer that has an input terminal and an output
terminal and has a microwave transistor.
[0057] Moreover, the microwave band radio communication system of
this invention comprises the microwave band radio transmitter and
the microwave band radio receiver.
[0058] According to the microwave band radio communication system
of the above-mentioned construction, the levels of the radio signal
wave to be transmitted, the local oscillation signal wave and the
unnecessary suppression signal wave can be accurately controlled,
and the radio transmission bandwidth and the transmission distance
can be extended.
[0059] Moreover, in one embodiment, the input modulation signal
wave of the microwave band radio transmitter is a signal wave
comprised of either one or a combination of two or more of a ground
wave TV broadcasting wave signal, a satellite broadcasting
intermediate frequency signal wave and a cable TV signal wave.
[0060] According to the microwave band radio communication system
of the above-mentioned embodiment, with the radio transmission
carried out by inputting to the microwave band radio transmitter a
signal comprised of any one or a combination of two or more of the
ground wave TV broadcasting signal wave, the satellite broadcasting
intermediate-frequency signal wave and the cable TV signal wave as
the input modulation signal wave, the ground wave TV broadcasting
signal wave, the satellite broadcasting intermediate-frequency
signal wave and the cable TV signal wave can be simultaneously
transmitted while being multiplexed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] FIG. 1 is a block diagram showing the construction of a
microwave band radio communication system of this invention;
[0062] FIG. 2 is a transmission spectrum of the microwave band
radio transmitter of the above microwave band radio communication
system;
[0063] FIG. 3 is a block diagram showing the construction of the
microwave band radio transmitter in which two frequency converting
sections are arranged in parallel with each other, and the
microwave band radio receiver of this invention,;
[0064] FIG. 4 is a graph showing the detection characteristic of
the frequency mixer of the above microwave band radio receiver;
[0065] FIG. 5 is a block diagram showing the construction of the
microwave band radio communication system of the first embodiment
of this invention;
[0066] FIG. 6 is a circuit diagram of an active mixer employed in
the microwave band radio receiver of the above microwave band radio
communication system;
[0067] FIG. 7 is a block diagram showing the construction of a
microwave band radio communication system of the second embodiment
of this invention;
[0068] FIG. 8 is a block diagram showing the construction of a
microwave band radio communication system of the third embodiment
of this invention;
[0069] FIG. 9 is a block diagram showing the construction of a
microwave band radio communication system of the fourth embodiment
of this invention;
[0070] FIG. 10 is a block diagram showing the other construction of
the above microwave band radio communication system;
[0071] FIG. 11 is a block diagram showing the construction of a
microwave band radio communication system of the fifth embodiment
of this invention;
[0072] FIG. 12 is a block diagram showing the construction of a
conventional microwave band radio communication system; and
[0073] FIG. 13 is a graph showing the relation of a frequency
spectrum in the above microwave band radio communication
system.
BEST MODE FOR CARRYING OUT THE INVENTION
[0074] Before describing embodiments of this invention, the
principle of the microwave band radio communication system of this
invention will be first described below with reference to FIGS. 1
through 4. FIG. 1 is a block diagram showing the construction of
the microwave band radio communication system, and FIG. 2 shows the
transmission spectrum of the microwave band radio transmitter shown
in FIG. 1. FIG. 3 is a block diagram showing the construction of a
microwave band radio transmitter in which two frequency converting
sections are arranged in parallel with each other, and a microwave
band radio receiver, and FIG. 4 is a graph showing the detection
characteristic of the frequency mixer of the microwave band radio
receiver shown in FIG. 3. In this embodiment, a radio communication
system that transmits and receives a radio signal wave in the
milliwave band will be described. The band of the radio signal wave
is not limited to the milliwave band, and this invention can be
applied to the microwave frequency band including the milliwave
band.
[0075] As shown in FIG. 1, an input modulation signal wave 108a is
frequency-upconverted to an intermediate frequency signal wave in a
first frequency converting section 18, and an intermediate
frequency multiplex signal wave 7 is generated by adding a sine
wave that contains a phase noise component and so on as a reference
signal wave to the frequency-upconverted intermediate frequency
signal. A radio multiplex signal wave 115 is generated by
frequency-upconverting the intermediate frequency multiplex signal
wave 7 to the milliwave band in a second frequency converting
section 19, and the radio multiplex signal wave 115 is transmitted.
In this case, by using the sine wave as the reference signal wave,
the signal of the desired wave can be frequency-downconverted by
using the sine wave on the reception side. This downconversion is
described in detail in the present specification. In addition, the
signal wave frequency-downconverted by the sine wave are dominated
by the frequency stability and the phase noise characteristic of
the sine wave itself, and therefore, it is possible to control the
frequency stability and the phase noise characteristic by using the
sine wave.
[0076] The above construction is able to solve the difficulties in
controlling the output levels of the local oscillation wave 106
(frequency: fLo), the radio signal wave 107 (frequency: fRF) and
the unnecessary one-side sideband signal wave on the transmission
side. That is, an intermediate frequency multiplex signal wave 7
(frequency: fIFmp) is generated by carrying out frequency
conversion to a second intermediate frequency (fIF1+fLO1) in the
first frequency converting section 18 by using a reference signal
source 14 (frequency: fLO1) that serves as a first local
oscillation source and thereafter adding thereto a reference signal
(frequency: fLO1) from the reference signal source 14. At this
time, the frequency-converted fIF1+fLO1 component and the fLO1
component of the reference signal wave exist in the intermediate
frequency multiplex signal wave 7 (frequency: fIFmp). Subsequently,
frequency conversion is carried out in the second frequency
converting section 19 by using a local oscillation source 17
(frequency: fLO2). The converted radio multiplex signal wave 115
(frequency: fRFmp) is constituted of the fIF1+fLO2+fLO1 component
of the desired radio signal wave 107 (frequency: fRF) and the
fLO2+fLO1 component of the desired radio reference signal wave 106
(frequency: fp).
[0077] FIG. 2 shows a frequency spectrum component after the first
and second frequency conversions. In this invention, the radio
signal wave 107 (frequency: fRF=fIF1+fLO2+fLO1) and the radio
reference signal wave 106 (frequency: fp=fLO2+fLO1) of the desired
waves can be separated from the fLO2 component of the second local
oscillation signal wave of the unnecessary wave and the
fLO2-(fLO1+fIF1) component of the unnecessary image signal wave
with regard to the frequency interval through the two-time
frequency conversions, and this enables suppression and filtering
in a second bandpass filter 9.
[0078] In concrete, assuming that the signal frequency fIF1 is 0.5
GHz to 1 GHz, the reference signal wave (frequency: fLO1) is 4 GHz
and the local oscillation wave (frequency: fLO2) is 55 GHz, then
the fLO1+fLO2 (=fp) component and the fLO2+fLO1+fIF (=fRF)
component in the radio multiplex signal wave 115 (frequency: fRFmp)
become 59 GHz and 59.5 GHz to 60 GHz, respectively, while the
frequency fLO2 of the unnecessary wave component becomes 55 GHz and
the frequency fLO2-(fLO1+fIF1) of the image signal wave becomes
54.0 GHz to 54.5 GHz. The frequency interval between the radio
reference signal wave 106 (frequency: fp) of the desired wave and
the local oscillation wave (frequency: fLO2) of the unnecessary
wave is separated by 4 GHz, and this enables filtering in the
second bandpass filter 9 that is the normal bandpass filter of the
milliwave band. This is clarified by comparison with the
conventional spectrum components (FIG. 13). For example, assuming
that the frequency fIF is 0.5 GHz to 1 GHz and the frequency
fLO=59.0 GHz, then the frequency fLO of the local oscillation wave
106b (radio signal wave) becomes 59.0 GHz, and the frequency
fLO-fIF of the image signal wave of the unnecessary wave becomes
58.0 GHz to 58.5 GHz. The frequency interval between them is only
0.5 GHz, and it is evident that the separation and filtering in the
second bandpass filter 9 are difficult.
[0079] In addition, in the above-mentioned construction, the second
intermediate frequency signal wave (frequency: fIF2=fLO1+fIF1) and
the reference signal wave (frequency: fLO1) inputted to the second
frequency converting section 19 can easily be subjected to level
control in the intermediate frequency stage of a low frequency by a
variable attenuator 12 (AGC (Automatic Gain Control) amplifier or
the like) (FIG. 1). This also makes it possible to control the
output levels of the radio signal wave 107 (frequency:
fRF=fLO1+fLO2+fIF) and the radio reference signal wave 106
(frequency: fp=fLO1+fLO2) after the second frequency
conversion.
[0080] In addition, it becomes possible to use a harmonic mixer
such as an even harmonic mixer for the second frequency converting
section 19 since the local oscillation wave (frequency: fLO) is not
directly used as a transmission wave. Although the local
oscillation frequency fLO2 of this construction has been 55 GHz
used in the aforementioned concrete example, an oscillation signal
of 5 GHz/2=27.5 GHz and 55 GHz/4=13.75 GHz can also be used.
Therefore, the circuit construction and the high frequency mounting
can be achieved remarkably easily at lower cost.
[0081] Further, by carrying out frequency conversion in the first
frequency converting section 18, the interval between the local
oscillation frequency fLO2 and the frequency fRF (=fLO1+fLO2+fIF1)
of the radio signal wave 107 becomes extended to fLO1+fIF1 (=fIF2).
Therefore, the influence of the nonlinearity of the second
frequency converting section 19 on the second intermediate
frequency signal wave 7 (frequency: fIF2=fIf1+fLO1) of the input
signal to the second frequency converting section 19 and on the
reference signal wave (frequency: fLO1), i.e., the influence of the
second, third, fourth, fifth, . . . components of the frequencies
of the local oscillation frequencies fLO1 and fIF2 can be ignored.
The reason for the above is that the frequency interval becomes
widened in the milliwave band obtained through the frequency
upconversion in the second frequency converting section 19, and
filtering can easily be achieved by the bandpass filter 9.
[0082] For example, assuming that the frequencies fLO1=4.0 GHz,
fIF2=4.5 GHz to 5.5 GHz and fLO2=55.0 GHz, then the frequency fp of
the radio reference signal wave becomes 59.0 GHz and the frequency
fRF of the radio signal wave becomes 59.5 GHz to 60.5 GHz through
the frequency upconversion by the second frequency converting
section 19. On the other hand, the second, third, . . . harmonic
components of the reference signal wave (frequency: fLO1) and the
second intermediate frequency signal wave (frequency: fIF2)
respectively become as follows.
[0083] 2*fLO1=8 GHz, 2*fIF2=9 GHz to 11 GHz,
[0084] 3*fLO1=12 GHz, 3*fIF2=13.5 GHz to 16.5 GHz,
[0085] By being frequency-upconverted to the milliwave band, fLO=55
GHz is added to these frequencies, so that frequency spectrum
components are generated at the frequencies of 63 GHz, 64 GHz to 66
GHz, 67 GHz and 68.5 GHz to 71.5 GHz. However, since the frequency
components are separated by at least 1.5 GHz or more apart from the
radio signal wave (frequency: fRF), the frequency components can
easily be suppressed by the bandpass filter 9, and the radio
transmission bandwidth can be consequently extended.
[0086] Furthermore, by employing an even harmonic mixer of an
anti-parallel type diode pair or the like for the second frequency
mixer 8, the second harmonic wave components of fIF2 and fLO1 can
be suppressed and removed by the operation of frequency
upconversion to the milliwave band. Therefore, in the
aforementioned example, the components of the frequencies of 63 GHz
and 64 GHz to 66 GHz are not outputted, and the radio transmission
bandwidth can be extended more accurately. When the transmission
bandwidth of the intermediate frequency signal wave (frequency:
fIF1) is further extended, it is also possible to extend the
transmission frequency band by arranging a 1b-th frequency
converting section 18b in parallel with the first frequency
converting section 18 as shown in FIG. 3. It is acceptable to
arrange two or more frequency converting sections in parallel with
the first frequency converting section 18 without limitation to the
case of two sections arranged in parallel.
[0087] On the other hand, by generating a first radio multiplex
signal wave 115 and a second radio multiplex signal wave 115b and
transmitting the respective signal waves in the forms of different
polarized waves, the transmission bandwidths of the intermediate
frequency signal wave that serves as a first input signal and the
intermediate frequency signal wave that serves as a second input
signal can be extended in the aforementioned milliwave band
transmitter. In concrete, by transmitting the first radio multiplex
signal wave 115 and the second radio multiplex signal wave 115b in
the forms of a vertically polarized wave and a horizontally
polarized wave, respectively, and receiving the first and second
radio multiplex signal waves 115 and 115b in the forms of the
vertically polarized wave and the horizontally polarized wave,
respectively, on the reception side, the transmission bandwidth can
be extended.
[0088] Moreover, in the milliwave band receiver, the radio
multiplex signal wave 115 transmitted from the transmission side is
frequency-downconverted by the radio reference signal wave 106
(frequency: fp) contained in the radio multiplex wave signal,
generating the intermediate frequency signal wave 108a. In this
case, the reception amplifier 21 serves as a variable gain
amplifier and is able to control the gain of the reception
amplifier 21 according to the output signal level of the
frequency-converted intermediate frequency signal wave (frequency:
fIF). With this arrangement, as indicated by the detection
characteristic of the frequency mixer 22 on the reception side in
FIG. 4, linear detection operation is achieved in the region where
the transmission distance is short and the reception level is very
large, while square-law detection operation can be achieved in the
region where the transmission distance is long and the reception
level is small.
[0089] That is, the low-noise reception amplifier 21 has an
automatic gain control (AGC) function. When the reception level is
small, the level of the input to the frequency mixer 22 is kept
constant by increasing the gain of the reception amplifier 21,
allowing the linear detection operation range to be extended. When
the reception level is too large, the nonlinear distortion caused
in the large signal region of the frequency mixer 22 and the
amplifier is reduced by reducing the gain of the amplifier 21 and
reducing the input level of the frequency mixer 22, so that a
stabilized reception level can be obtained.
[0090] Furthermore, it is also possible to achieve improvement with
the construction of a two-terminal type frequency mixer 22 that
employs a microwave transistor in the milliwave radio receiver. The
frequency mixer 22 is allowed to be a two-terminal mixer that has
two terminals of an input terminal and an output terminal.
Dissimilarly to a normal three-terminal type frequency mixer that
has a local oscillation LO port, a radio frequency RF port and an
intermediate frequency IF port, there is no need of a circuit that
separates the RF port from the LO port at the input port, and in
particular, the performance of the frequency mixer of the microwave
transistor type that has a low conversion loss can be further
improved. That is, by inputting the radio multiplex signal wave 115
to the input terminal and providing a short-circuit stub as one
example of the short-circuit circuit that is short-circuited at the
radio multiplex wave signal frequency in the output section of the
microwave transistor, the internal operation of the transistor
shifts to larger signal operation through the reflection and
feedback of the radio multiplex signal wave 115 to the output
terminal of the microwave transistor to widen the linear detection
operation region in FIG. 4, and the radio transmission distance can
be extended.
[0091] Furthermore, it is also possible to extend the linear
operation region by employing a heterojunction type bipolar
transistor (HBT) for the microwave transistor. This is because the
internal operation of the transistor tends to easily enter the
large signal operation region due to a large mutual conductance
possessed by the HBT in comparison with FET and so on and the
linear detection operation region can be consequently extended.
[0092] In addition, by transmitting the radio reference signal wave
106 (frequency: fp) in the radio multiplex signal wave 115 at a
level at least 3 dB or more higher than that of the radio signal
wave 107 (frequency: fRF) on the milliwave band transmitter side,
the linear operation region of the frequency mixer 22 on the
reception side can be extended. That is, the radio signal wave
(frequency: fRF) is normally a multiple (multi-channel) modulation
signal wave, and the total power level of the radio signal wave of
a wide bandwidth is large in comparison with the radio reference
signal wave 106 of the reference frequency fp. Therefore, by making
the level of the radio reference signal wave (frequency: fp)
sufficiently larger, i.e., at least 3 dB or more larger than the
total power of the radio signal wave (frequency: fRF) to operate
the frequency mixer 22 with a large signal by the radio reference
signal wave (frequency: fp), the linear detection operation region
can be extended.
[0093] The microwave band radio transmitter, the microwave band
radio receiver and the microwave band radio communication system of
this invention will be described in detail below on the basis of
the embodiments shown in the drawings.
First Embodiment
[0094] FIG. 5 is a block diagram showing the construction of the
microwave band radio communication system of the first embodiment
of this invention, and this microwave band radio communication
system is constructed of a microwave band radio transmitter and a
microwave band radio receiver. In FIG. 5, the components that
operate and function similarly to those of FIGS. 1 through 4 are
denoted by the same reference numerals.
[0095] As shown in FIG. 5, in the above-mentioned microwave band
radio transmitter, an intermediate frequency signal wave 108a
(frequency: fIF1) modulated by an IF modulation signal source 100
is generated and inputted to a first frequency converting section
18. Next, the signal wave is inputted to a frequency mixer 3 that
serves as the first frequency converting means at an appropriate
level via a bandpass filter 1 and a variable amplifier 2, and the
intermediate frequency signal wave 108a is frequency-upconverted to
a second intermediate frequency signal wave (frequency: fIF2) by
the frequency mixer 3 by using a reference signal wave (frequency:
fLO1) from the reference signal source 14. The
frequency-upconverted second intermediate frequency signal wave
(frequency: fIF2) has a signal of either the upper sideband or the
lower sideband selected by a first bandpass filter 13 and has the
unnecessary signal waves of the second, third and distortion
component signals and so on of the first intermediate frequency
signal wave 108a (frequency: fIF1) removed. In this first
embodiment, the signal of the upper sideband is selected as the
second intermediate frequency signal wave, and the relation of
frequency fIF2=fLO1+fIF1 of the second intermediate frequency
signal wave is possessed.
[0096] The second intermediate frequency signal wave (frequency:
fIF2) is amplified to an appropriate level by an amplifier 4 and
combined with the reference signal wave (frequency: fLO1) by a
signal combiner 5a to generate an intermediate frequency multiplex
signal wave 7 (frequency: fIFmp). When the intermediate frequency
multiplex signal wave 7 (frequency: fIFmp) is made, the reference
signal source 14 constructed of a phase locked oscillator (PLO), a
temperature compensation type crystal oscillator (TCXO) or the like
is stabilized by the temperature compensation type crystal
oscillator (TCXO). The reference signal wave (frequency: fLO1) is
distributed by a signal distributor 5b, so that one signal is
supplied to the frequency mixer 3 and the other signal is
controlled to an appropriate level by the variable attenuator 12
(or a variable amplifier) or the like and combined with the second
intermediate frequency signal wave (frequency: fIF2) by the signal
combiner 5a.
[0097] In this case, the signal combiner 5a has a construction in
which the input signals are prevented from flowing into irrelevant
ports by using a signal combiner whose input terminals of a
Wilkinson-type combiner, a branch-line type combiner or the like
are mutually isolated. It is to be noted that the signal combiner
5a may be constructed of a circulator. On the other hand, the
signal distributor 5b has a construction in which the signals
distributed into two ways have the desired power levels and are
prevented from flowing into irrelevant signal ports by using a
signal distributor whose output terminals of a Wilkinson-type
divider, a branch-line type distributor or the like are mutually
isolated.
[0098] In this first embodiment, the first intermediate frequency
signal wave 108a (frequency: fIF1) is a signal of 500 MHz to 1500
MHz, the reference signal wave (frequency: fLO1) is a signal of
3400 MHz, and the second intermediate frequency signal wave
(frequency: fIF2) is a signal of 3900 MHz to 4900 MHz. The
intermediate frequency multiplex signal wave 7 (frequency: fIFmp)
is a signal of 3400 MHz to 4900 MHz.
[0099] In this case, the following operation is carried out during
the first frequency conversion (note that the symbol: a .epsilon. B
indicates ones "a" that belong to a set B as the element of the set
B).
[0100] (1-1) First Frequency Conversion 1 fIF2 = fLO1 + fIF1 = 3400
MHz + ( 500 MHz to 1500 MHz ) = 3900 MHz to 4900 MHz
[0101] (1-2) Generation of Multiplex Wave in IF Stage fLO1, fIF2
.epsilon. fIFmp
[0102] The intermediate frequency multiplex signal wave 7
(frequency: fIFmp) is inputted to the second frequency converting
section 19 and frequency-upconverted to the milliwave band by the
second frequency mixer 8 that serves as the second frequency
converting means and a local oscillator 11. Either the upper
sideband signal or the lower sideband signal is selected by the
second bandpass filter 9, and the unnecessary wave signal
accompanying the second frequency conversion are suppressed. In
this first embodiment, the lower sideband is suppressed, and the
upper sideband is used. Then, the signal wave filtered by the
second bandpass filter 9 is amplified by a transmission amplifier
10 and transmitted as a radio multiplex signal wave 115 (frequency:
fRFmp) from a transmission antenna 15.
[0103] The multiplex wave generating means is constituted of the
signal combiner 5a and the attenuator 12, while the transmission
means is constituted of the transmission amplifier 10 and the
transmission antenna 15.
[0104] In this first embodiment, the local oscillation frequency of
the local oscillator 11 is a local oscillation frequency of a half
of the oscillation frequency fLO2 of the fundamental wave mixer
employed in the conventional milliwave band transmitter (shown in
FIG. 12) by employing an even harmonic mixer constructed of an
anti-parallel diode pair for the second frequency mixer 8, and a
signal of fLOH=27.8 GHz is used. In this case, the frequency fRFmp
of the radio multiplex signal wave 115 becomes 59 GHz to 60.5 GHz,
the frequency fp of the radio reference signal wave 106 becomes
59.0 GHz, and the frequency fRF of the radio signal wave 107
becomes 59.5 GHz to 60.5 GHz.
[0105] In this case, the following operation is carried out in the
second frequency converting section 19.
[0106] (2-1) Frequency Conversion of Reference Signal Wave 2 fp =
fLO1 + fLO2 = fLO1 + fLOH * 2 = 3.4 GHz + 27.8 GHz * 2
[0107] (2-2) Frequency Conversion of Radio Signal 3 fRF = fIF2 +
fLO2 = fIF2 + fLOH * 2 = ( 0.5 GHz to 1.5 GHz ) + 27.8 GHz * 2 =
59.5 GHz to 60.5 GHz
[0108] (2-3) Radio Multiplex Wave Signal fRF, fp .epsilon.
fRFmp
[0109] By thus constituting the microwave band radio transmitter,
it becomes extremely easy to control the output levels of the radio
reference signal wave 106 (frequency: fp), the radio signal wave
107 (frequency: fRF) and the unnecessary one-side sideband signal
wave. That is, in the aforementioned microwave band radio
transmitter, the second intermediate frequency signal wave
(frequency: fIF2=fLO1+fIF1) inputted to the second frequency
converting section 19 and the first intermediate frequency
reference signal wave (frequency: fLO1) have their levels
controllable by the variable amplifier 2 and the variable
attenuator 12 (AGC amplifier or the like) which are provided in the
input stage, so that the powers of the second local oscillation
frequencies fLO2 and fLOH can be made constant and fixed. With this
arrangement, the output levels of the desired radio signal wave 107
(frequency: fLO1+fLO2+fIF) after the second frequency conversion
and the desired radio reference signal wave 106 (frequency:
fLO1+fLO2) can also be controlled.
[0110] In addition, in the second frequency converting section 19,
the local oscillation wave (frequency: fLO2) itself contributes
only to the second frequency conversion instead of the radio
multiplex signal wave 115 (frequency: fRFmp) radiated directly from
the transmitter, and therefore, it becomes possible to utilize also
a harmonic mixer such as an even harmonic mixer for the second
frequency mixer 8. Therefore, not only the fundamental oscillation
wave fLO2=55.6 GHz but also the oscillation signals of 55.6
GHz/2=27.8 GHz and 55.6 GHz/4=13.9 GHz can be used for the local
oscillation frequency. Therefore, the circuit construction and high
frequency mounting become remarkably easy.
[0111] Further, by carrying out frequency conversion in the first
frequency converting section 18, the interval between the frequency
fLO2 of the local oscillation wave and the frequency fRF
(=fLO1+fLO2+fIF1) of the radio signal wave 107 is increased to
fLO1+fIF1 (=fIF2). Therefore, if the second, third, fourth, fifth,
. . . components of the frequencies fLO1 and fIF2 are
disadvantageously outputted due to the influence of the
nonlinearity of the frequency mixer 8 on the second intermediate
frequency fIF2 (=fIf1+fLO1) that is the input signal to the second
frequency converting section 19 and the reference signal wave
(frequency: fLO1), the frequency interval becomes widened in the
milliwave band frequency-upconverted by the second frequency
converting section 19, and suppression can easily be achieved by
the second bandpass filter 9.
[0112] For example, assuming that fLO2=4.0 GHz, fIF2=4.5 GHz to 5.5
GHz and fLO2=55.0 GHz, then the frequency fp of the radio reference
signal wave becomes 59.0 GHz and the frequency fRF of the radio
signal wave becomes 59.5 GHz to 60.5 GHz through the frequency
upconversion by the second frequency converting section 19. On the
other hand, the second, third, . . . harmonic components of the
reference signal wave (frequency: fLO1) and the second intermediate
frequency signal wave (frequency: fIF2) respectively become as
follows.
[0113] 2*fLO1=8 GHz, 2*fIF2=9 GHz to 11 GHz,
[0114] 3*fLO1=12 GHz, 3*fIF2=13.5 GHz to 16.5 GHz,
[0115] Therefore, by carrying out the frequency upconversion to the
milliwave band, fLO=55 GHz is added to these frequencies, and
frequency spectrum components are generated at the frequencies of
63 GHz, 64 GHz to 66 GHz, 67 GHz and 68.5 GHz to 71.5 GHz. However,
because of the separation from the radio signal wave (frequency:
fRF) by at least 1.5 GHz or more, those components can easily be
suppressed by the second bandpass filter 9. As a result, the radio
transmission bandwidth can be extended. In addition, by employing
an even harmonic mixer of an anti-parallel type diode pair or the
like for the second frequency mixer 8, the second harmonic
components of the second intermediate frequency fIF2 and the
frequency fLO1 of the reference signal wave can be suppressed and
removed by the operation of frequency upconversion to the milliwave
band. Therefore, in the aforementioned concrete example, there is
no possibility of the output of the components of 63 GHz and 64 GHz
to 66 GHz, and the radio transmission bandwidth can be extended
more accurately.
[0116] If the first intermediate frequency fIF1 is set to 0.5 GHz
to 1.5 GHz, then the influences of the generation of the higher
harmonics due to the first frequency mixer 3 in the first frequency
converting section 18 are removed. This is because the frequency
mixer 3 whose input and output frequencies are low is allowed to
have a double-balanced mixer construction, and therefore, the
suppression of the secondary distortion is sufficient, making it
possible to achieve further suppression and removal by the bandpass
filter 13.
[0117] On the other hand, in the aforementioned microwave band
radio receiver, the wirelessly transmitted radio multiplex signal
wave 115 is received by the reception antenna 20 and amplified by
the low-noise reception amplifier 21. The signal of the desired
passband (59.0 GHz to 60.5 GHz in the first embodiment) is filtered
by the second band-pass filter 9 and frequency-downconverted by the
frequency mixer 22. In the operation of frequency downconversion, a
first intermediate frequency signal wave 108b (frequency: fIF1) is
generated by carried out the frequency downconversion of the radio
signal wave 107 (frequency: fRF) by the radio reference signal wave
106 (frequency: fp) in the radio multiplex signal wave 115. In this
first embodiment, the frequency fIF1 of the first intermediate
frequency signal wave 108b is set to 500 MHz to 1500 MHz. The first
intermediate frequency signal wave 108b (frequency: fIF1) is
amplified to an appropriate level by an amplifier 23, and the
signal waves other than those in the above-mentioned band (500 MHz
to 1500 MHz) are suppressed by a bandpass filter 24. After passing
through the bandpass filter 24, the signal wave is inputted to the
demodulator and tuner 113.
[0118] In this case, the following operation is carried out during
the frequency downconversion on the reception side. 4 fIF1 = fRF -
fp = ( 59.5 GHz to 60.5 GHz ) - 59.0 GHz = 0.5 GHz to 1.0 GHz
[0119] The frequency mixer 22 carries out the frequency
downconversion of the radio signal wave 107 (frequency: fRF) by the
radio reference signal wave 106 (frequency: fp) in the radio
multiplex signal wave 115. In the above stage, although the linear
detection is conducted in the region where the reception level is
very large, the square-law detection is conducted in the region
where the reception level is small. That is, in the frequency mixer
22, the radio reference signal wave 106 (frequency: fp) operates at
a large signal level in the linear detection region, and therefore,
frequency mixing is carried out depending on the input level of the
radio signal wave 107 (frequency: fRF) without depending on the
level of the radio reference signal wave 106 (frequency: fp).
Therefore, if the level of the radio multiplex signal wave 115 at
the input level is reduced by 6 dB, then the first intermediate
frequency signal wave 108b (frequency: fIF1) of the output is
reduced by 6 dB. On the other hand, in the region where the radio
transmission distance is elongated and the reception level is
reduced, the radio reference signal wave 106 (frequency: fp) and
the radio signal wave 107 (frequency: fRF) operate with small
signals in the frequency mixer 22, and the reductions in the levels
of both the signal waves influence the output level of the
intermediate frequency signal wave 108b (frequency: fIF1).
Consequently, the frequency downconversion is carried out depending
on the levels of both the input level of the radio signal wave 107
(frequency: fRF) and the level of the radio reference signal wave
106 (frequency: fp). Therefore, if the radio multiplex signal wave
115 is reduced by 6 dB as the input level of the frequency mixer
22, i.e., if the radio reference signal (frequency: fp) and the
radio signal wave (frequency: fRF) are each reduced by 6 dB, then
the first intermediate frequency signal wave 108b (frequency: fIF1)
of the output is reduced by 12 dB.
[0120] In the aforementioned first embodiment, by preferably using
an active mixer including a microwave transistor for the frequency
mixer 22, it becomes possible to extend the linear detection
operation region. FIG. 6 shows the concrete circuit construction of
the active mixer on the reception side. The operation of the active
mixer employed as the frequency mixer 22 will be described with
reference to FIGS. 5 and 6.
[0121] The radio multiplex signal wave 115 that has passed through
the bandpass filter 9 on the reception side, i.e., the radio
reference signal wave 106 (frequency: fp=fLO1+fLO2) and the radio
signal wave 107 (frequency: fRF=fLO1+fLO2+fIF1) are inputted to an
input port 41 and matched with the input impedance of a microwave
transistor 43 by an RF.andgate.LO matching circuit 44. In the
microwave transistor 43, the radio reference signal wave 106
(frequency: fp) operates as a local oscillation wave to
frequency-downconvert the radio signal wave 107 (frequency: fRF) to
the first intermediate frequency signal wave 108b (frequency:
fIF1). The frequency-downconverted first intermediate frequency
signal wave 108b (frequency: fIF1) is outputted from an output port
42 via an RF.cndot.LO short-circuit circuit 48 on the output side
of the microwave transistor 43 and an output circuit 45. The output
circuit 45 is a circuit that further suppresses the RF.cndot.LO
signal and converts the converted IF signal into an appropriate
impedance (e.g., high impedance). In this case, the RF.cndot.LO
short-circuit circuit 48 including a transmission line 46, an open
stub 47 or the like is provided in the vicinity of the output
terminal of the microwave transistor 43. By making both the signal
waves of the radio reference signal wave 106 (frequency: fp) that
serves as the outputted local oscillation wave in the milliwave
band and the radio signal wave 107 (frequency: fRf) have a
short-circuit impedance at a connection point 47P of the open stub
47 and the transmission line 46, adjusting them to an appropriate
phase by the transmission line 46 and feeding them back to the
microwave transistor 43, the internal operation of the microwave
transistor 43 is shifted to larger signal operation.
[0122] The linear detection operation is achieved with respect to
the smaller input level of the radio multiplex signal wave 115 by
the RF.cndot.LO short-circuit circuit 48, and therefore, the
frequency conversion efficiency of this frequency mixer 22 to the
intermediate frequency fIF can be increased. Dissimilarly to the
generally employed three-terminal type mixer that has an LO port,
an RF port and an IF port, there are provided advantages that a
circuit for separating the RF port from the LO port in the input
port becomes unnecessary, and the performance of the microwave
transistor type frequency mixer that has a low conversion loss can
be sufficiently produced.
[0123] Furthermore, in the aforementioned microwave band radio
receiver, the radio signal wave 107 (frequency: fRf) is
frequency-downconverted by the radio reference signal wave 106
(frequency: fp) in the radio multiplex signal wave 115. Therefore,
dissimilarly to the operation of the normal three-terminal mixer,
the reference signal wave (operating as the local oscillation
signal) level is small. Therefore, by making the microwave
transistor 43 have an electrode size (gate width in an FET or
emitter size in a bipolar transistor) fifty percent smaller than
the size of the electrode employed in the normally employed
three-terminal mixer, the internal operation of the microwave
transistor 43 tends to easily shift to larger signal operation even
also with respect to a smaller radio reference signal wave 106
(frequency: fp), allowing the conversion efficiency to be further
increased. By reducing the frequency conversion loss on the
reception side and extending the linear detection operation region
with the above-mentioned construction, it becomes possible to
extend the radio transmission distance.
[0124] In addition, this microwave band radio receiver can further
extend the linear operation region by using a heterojunction type
bipolar transistor (HBT) for the microwave transistor 43. This is
because the transistor (HBT) can internally enter a large signal
operation region due to the large mutual conductance possessed by
the HBT in comparison with FET or the like, and it consequently
becomes possible to extend the linear detection operation
region.
[0125] Furthermore, in the microwave band radio transmitter, the
linear operation region of the frequency mixer 22 on the reception
side can be extended by transmitting the radio reference signal
wave 106 (frequency: fp) in the radio multiplex signal wave 115 at
a level at least 3 dB or more higher than that of the radio signal
wave 107 (frequency: fRF). That is, the radio signal wave
(frequency: fRF) is normally a multiple (multi-channel) modulation
signal wave, and its bandwidth is wide and the total power level of
the radio signal wave is large by comparison with those of the
reference frequency fp. Therefore, by making the frequency mixer 22
carry out large signal operation with respect to the radio
reference signal wave (frequency: fp) by making the level of the
radio reference signal wave (frequency: fp) sufficiently larger
than the total power of the radio signal wave (frequency: fRF),
i.e., making the level larger by at least 3 dB or more, the linear
detection operation region can be extended.
[0126] Furthermore, in this microwave band radio receiver, the
linear detection region of the frequency mixer 22 can be extended
also by controlling the gain of the reception amplifier 21 which is
the variable gain amplifier according to the output signal level of
the frequency-converted intermediate frequency signal wave
(frequency: fIF). As shown in FIG. 5, after the intermediate
frequency signal (frequency: fIF1) frequency-converted by the
frequency mixer 22 on the reception side is amplified to the
appropriate level by the amplifier 23, the fIF signal is
distributed to constitute a negative feedback loop of a detector 87
for detecting the envelope, an amplifier 86 and a low-pass filter
85, and the gain of the reception amplifier 21 is controlled. This
makes it possible to adjust the amplification degree of the
reception amplifier 21 in accordance with the output level of the
frequency-downconverted intermediate frequency (frequency: fIF1)
and supply an input signal (115) at a constant level to the
frequency mixer 22. Therefore, in the case where no automatic gain
control function is provided like the detection characteristic of
the frequency mixer 22 on the reception side shown in FIG. 4, the
linear detection operation is carried out in the region where the
transmission distance is short and the reception level is very
large. In the region where the transmission distance is long and
the reception level is small, the square-law detection operation is
carried out. On the other hand, by virtue of the low-noise
reception amplifier 21 that has an automatic gain control (AGC)
function, it becomes possible to extend the linear detection region
by increasing the gain of the reception amplifier 21 and increasing
the level of the input to the frequency mixer 22 when the reception
level is small. Furthermore, when the reception level is too large,
it becomes possible to keep the input level constant by reducing
the gain of the reception amplifier 21 and reducing the input level
of the frequency mixer 22 and obtain a stabilized reception level
by reducing the nonlinear distortion caused in the large signal
regions of the frequency mixer 22 and the amplifier.
Second Embodiment
[0127] FIG. 7 is a block diagram showing the construction of a
microwave band radio communication system of a second embodiment of
this invention, and this microwave band radio communication system
is constructed of a microwave band radio transmitter and a
microwave band radio receiver. The microwave band radio
communication system of this second embodiment has the same
construction as that of the microwave band radio communication
system of the first embodiment except for a local oscillator for
the second frequency converting section 19. The same components are
denoted by same reference numerals, and no description is provided
therefor. The section different from the first embodiment will be
described below.
[0128] Although the local oscillator 11 (shown in FIG. 5) entirely
independent of the reference signal source 14 of the first
frequency converting section 18 has been employed in the second
frequency converting section on the transmission side in the
aforementioned first embodiment, this second embodiment employs a
frequency multiplier 17 as a local oscillator for the second
frequency converting section 19. With this arrangement, the stable
reference signal from the reference signal source 14 can be used,
and this makes it possible to simply constitute a stable device
without needing an independent oscillation source of a high
frequency.
Third Embodiment
[0129] FIG. 8 is a block diagram showing the construction of a
microwave band radio communication system of a third embodiment of
this invention, and this microwave band radio communication system
is constructed of a microwave band radio transmitter and a
microwave band radio receiver. The microwave band radio
communication system of this third embodiment has the same
construction as that of the microwave band radio communication
system of the second embodiment except for an IF modulation signal
source 100b and a 1b-th frequency converting section 18b. The same
components are denoted by same reference numerals, and no
description is provided therefor. The sections different from the
second embodiment will be described below.
[0130] As shown in FIG. 8, an IF modulation signal wave (frequency:
fIF1b) is inputted from the IF modulation signal source 100b to the
1b-th frequency converting section 18b, and the signal wave is
subjected to 1b-th frequency upconversion by using the local
oscillation wave (frequency: fLO1) from the reference signal source
14 to generate a 2b-th intermediate frequency signal wave
(frequency: fIF2b=fLO1+fIF1b). Then, the 2b-th intermediate
frequency signal wave (frequency: fIF2b) is combined with the
second intermediate frequency signal wave (frequency:
fIF2=fLO1+fIF) that is the signal from the first frequency
converting section 18 and the local oscillation wave (frequency:
fLO1) from the reference signal source 14 by a signal combiner 5a
and inputted as the intermediate frequency multiplex signal wave 7
to the second frequency converting section 19.
[0131] In the second frequency converting section 19, the
intermediate frequency multiplex signal wave 7 (frequency:
fIF1+fLO1 and fIF1b+fLO1) and the reference signal wave (frequency:
fLO1) are frequency-upconverted to the milliwave band by using a
second local oscillation wave (frequency: fLO2). By suppressing the
unnecessary waves by the bandpass filter 9, there are generated the
radio signal wave 107 (frequency: fRF=fIF1+fLO1+fLO2), a radio
signal wave 107b (frequency: fRFb=fIF1b+fLO1+fLO2) and a radio
reference signal wave 106 (frequency: fp=fLO1+fLO2). The radio
signal waves 107 and 107b and the radio reference signal wave 106
are inputted to the transmission amplifier 10 of the milliwave
band, amplified to an appropriate level and thereafter radiated as
the radio multiplex signal wave 115 from the transmission antenna
15.
[0132] As described above, the frequency bandwidth of the
transmission band can be extended by arranging the first frequency
converting section 18 and the 1b-th frequency converting section
18b in parallel with each other, and a great amount of information
of, for example, the signals of the ground wave TV broadcasting,
the satellite broadcasting and so on can be multiplexed. In this
case, the reference signal wave (frequency: fLO1) is one-system
one-kind single frequency, which functions as a local oscillation
frequency fLO1 for carrying out frequency upconversion by means of
the frequency mixer 3 and a frequency mixer 3b and functions as a
reference signal wave (frequency: fLO1) to be multiplexed with the
second intermediate frequency signal wave (frequency: fIF2) and the
2b-th intermediate frequency signal wave (frequency: fIF2b). It is
to be noted that two or more frequency converting sections may be
arranged in parallel with the first frequency converting section
18.
Fourth Embodiment
[0133] FIG. 9 is a block diagram showing the construction of a
microwave band radio communication system of a fourth embodiment of
this invention, and this microwave band radio communication system
is constructed of a microwave band radio transmitter and a
microwave band radio receiver. In the microwave band radio
communication system of this fourth embodiment, the same
constructions as those of the microwave band radio communication
system of the second embodiment are denoted by same reference
numerals, and no description is provided therefor. The section
different from that of the second embodiment will be described
below.
[0134] As shown in FIG. 9, another system of an IF modulation
signal source 100b, a 1b-th frequency converting section 18b and a
2b-th frequency converting section 19b, which have the same
constructions as those of the IF modulation signal source 100, the
first frequency converting section 18 and the second frequency
converting section 19, is added. The reference signal wave
(frequency: fLO1) is supplied from the reference signal source 14
to both of the first frequency converting section 18 (including a
reference signal multiplex section and the 1b-th frequency
converting section 18b (including a reference signal multiplex
section). In both the sections, the reference signal wave
(frequency: fLO1) is multiplexed after the first and 1b-th
frequency conversions. Further, the signal wave (frequency:
fIF1+fLO) once subjected to the first frequency conversion and the
reference signal wave (frequency: fLO1) are inputted to the second
frequency converting section 19, while the other signal wave of
fIFb+fLO that has been subjected to the 1b-th frequency conversion
and the reference signal wave (frequency: fLO1) are inputted to the
2b-th frequency converting section 19. The signal waves are
frequency-converted to the milliwave band by both the second
frequency converting sections 19 and 19b, and a radio multiplex
signal wave 115 (fLO1+fLO2 and fLO1+fLO2+fIF1) and a radio
multiplex signal wave 115b (fLO1+fLO2 and fLO1+fLO2+fIF1b) are
independently radiated from the independent transmission antennas
15 and 15b, respectively.
[0135] In this case, during the second and 2b-th frequency
conversions, the local oscillation wave (frequency: fLO2) from the
frequency multiplier 17 that serves as a local oscillator is
inputted to both the second frequency converting section 19 and the
2b-th frequency converting section 19b. In this case, the reference
signal source 14 (frequency: fLO1) functions as the local
oscillation source of the first and 1b-th frequency converting
sections 18 and 18b (including a reference signal multiplex
section), while the frequency multiplier 17 (oscillation frequency:
fLO2) functions as the local oscillation source of the second and
2b-th frequency converting sections. Furthermore, in this fourth
embodiment, the transmission antenna 15 of vertically polarized
waves is employed for the second frequency converting section 19,
and the transmission antenna 15b of horizontally polarized waves is
employed for the 2b-th frequency converting section 19b. However,
it is acceptable to employ a right hand circular polarized wave
antenna and a left hand circular polarized wave antenna.
[0136] A milliwave band transmission means is constituted of the IF
modulation signal source 100, the first frequency converting
section 18 and the second frequency converting section 19, while a
milliwave band transmission means is constituted of the IF
modulation signal source 100b, the 1b-th frequency converting
section 18b and the 2b-th frequency converting section 19b of the
same constructions.
[0137] In the above-mentioned microwave band radio transmitter, the
level of the reference signal wave (frequency: fLO1) to be
multiplexed can be subjected to independent level adjustment by the
variable attenuators 12 and 12b, variable amplifiers and the like.
This is because the reference signal multiplex level differs from
the power level of multiplex wave generation by the reference
signal wave (frequency: fLO1) due to the modulation systems and the
transmission bandwidths of the IF modulation signal sources 100 and
100b.
[0138] Even in the above-mentioned microwave band radio receiver,
mutually different polarized waves are received by the reception
antennas 20 and 20b and frequency-converted by different frequency
converting sections 25 and 25b to obtain intermediate-frequency
signal waves IF1 and IF1b, which are inputted to the respective
demodulators and tuners 113 and 113b.
[0139] Even the construction of the fourth embodiment produces the
effects that the frequency range of the transmission band can be
extended and a great amount of information can be transmitted. For
example, by transmitting the ground wave TV broadcasting through
frequency conversion by the system of the first frequency
converting section 18 and the second frequency converting section
19 while transmitting the signal of the satellite broadcasting or
the like through frequency conversion by the system of the 1b-th
frequency converting section 18b and the 2b-th frequency converting
section 19b, the ground wave TV broadcasting and the satellite
broadcasting can be simultaneously transmitted.
[0140] Dissimilarly to the aforementioned third embodiment, the IF
modulation signals (frequencies: fIF1 and fIFb), of which the
reference signal level (frequency: fLO1) can be independently
multiplexed, are transmitted by mutually independent transmission
antennas 15 and 15b and the reception antennas 20 and 20b and
independently frequency-converted with independent bandwidths by
the frequency converting sections 25 and 25b that serve as the
milliwave band reception means. Accordingly, there is no need to
adjust the power levels of the combining circuit and signals on the
transmission side, while the branching circuit can be obviated on
the reception side. For example, in the case of the aforementioned
TV signal, an ordinary home normally has mutually independent
antenna terminals of the ground wave broadcasting and the satellite
broadcasting. There are provided the advantages that the ground
wave broadcasting output terminal and the satellite broadcasting
output terminal can be connected to the input terminals 71 and 71b
of the milliwave transmitter, and the output terminals 72 and 72b
in the microwave band radio receiver on the reception side are
directly connected to the tuner input terminals of the ground wave
broadcasting and the satellite broadcasting, respectively, on the
TV side.
[0141] Furthermore, in this fourth embodiment, the milliwave band
transmission means of both the systems have the construction in
which the radio reference signal waves 106 and 106b and the radio
signal waves 107 and 107b are multiplexed to constitute the radio
multiplex signal waves 115 and 115b, and the radio signal waves 107
and 107b are frequency-downconverted by the transmitted radio
reference signal wave (frequency: fLO1+fLO2) together with the
respective frequency converting sections 25 and 25b on the
reception side. However, as shown in FIG. 10, even with a microwave
band radio transmitter construction in which a radio signal wave
107c (frequency: fLO1+fLO2+fIFb) is transmitted as a third radio
signal without multiplexing the radio reference wave 106b in one
transmission system 18b, 19c, and the radio signal is
frequency-downconverted by a local oscillator 17c (frequency:
fLO1+fLO2) on the reception side, there are produced the advantages
that the transmission bandwidth can be extended, and the input
terminals 71 and 71b and the output terminals 72 and 72b can be
made independent on both the transmission side and the reception
side.
Fifth Embodiment
[0142] FIG. 11 is a block diagram showing the construction of a
microwave band radio communication system of a fifth embodiment of
this invention, and this microwave band radio communication system
is constructed of a microwave band radio transmitter and a
microwave band radio receiver. The microwave band radio transmitter
of this fifth embodiment has the same construction as that of the
microwave band radio transmitter of the first embodiment. The same
components are denoted by same reference numerals, and no
description is provided therefor. The section different from the
first embodiment will be described below.
[0143] As shown in FIG. 11, the microwave band radio receiver on
the reception side is constructed of a first frequency converting
section 76 and a second frequency converting section 75. The radio
multiplex signal wave 115 (frequency: fRFmp) transmitted from the
transmission side is received by the reception antenna 20 and
amplified by the reception amplifier 21. A second intermediate
frequency multiplex signal wave (frequency: fIFmp2) is generated by
passing only the radio multiplex signal wave 115 (frequency: fRFmp)
of the desired wave through the bandpass filter 9 and thereafter
frequency-downconverting the signal wave by the frequency mixer 22
by using an independent local oscillator 17c (frequency: fLO3) on
the reception side. The second intermediate frequency multiplex
signal wave (frequency: fIFmp2) frequency-converted by the first
frequency converting section 76 is constituted of an intermediate
frequency signal wave (frequency: fIF2) and a reference signal wave
(frequency: fLO4) and has the following relations with respect to
the transmission side.
[0144] (3-1) First Frequency Downconversion (fIFmp2 is Generated
from fRFmp)
[0145] Generation of fIF2, fLO4 .epsilon. fIFmp2 from fRF, fp
.epsilon. fRFmp
where fRF=(fLO1+fLO2)+fIF1
fp=(fLO1+fLO2)
[0146] (i) First frequency downconversion of radio signal wave 107
(Frequency: fRF) 5 fIF2 = fRF - fLO3 = ( fLO1 + fLO2 + fIF1 ) -
fLO3 = ( fLO1 + fIF1 ) + fLO where .DELTA.fLO=fLO2-fLO3
[0147] (ii) First frequency downconversion of radio reference
signal wave 106 (frequency: fp) 6 fLO4 = fp - fLO3 = ( fLO1 + fLO2
) - fLO3 = fLO1 + fLO
[0148] After carrying out the first frequency downconversion by
using the local oscillation signal fLO3 of the first frequency
converting section 76 on the reception side, the second
intermediate frequency multiplex signal wave (frequency: fIFmp2) is
branched into an intermediate frequency signal wave (frequency:
fIF2) and a reference signal wave (frequency: fLO4) by a branching
filter 74 of the second frequency converting section 75.
Thereafter, the first intermediate frequency signal wave
(frequency: fIF1) is generated by a second frequency mixer 82. The
first frequency downconversion and the second downconversion have
the following relations.
[0149] (3-2) Wave Branching and Second Frequency Conversion
[0150] Generation of fIF from fIF2, fLO4 .epsilon. fIFmp2
[0151] (i) fIF2 and fLO4 are separated by wave branching
[0152] (ii) Second frequency conversion (fIF1 is generated from
fIF2) 7 fIF1 = fIF2 - fLO4 = ( fLO1 + fIF1 ) + fLO - ( fLO1 + fLO )
= fIF1
[0153] According to the above-mentioned relations, the first
intermediate frequency signal wave 108b (frequency: fIF1) on the
transmission side can be finally reproduced on the reception
side.
[0154] In the above construction, it becomes possible to extend the
radio transmission distance since the linear detection is achieved
by carrying out the first frequency downconversion by means of the
independent local oscillator 17c, concurrently with reducing the
frequency conversion loss on the reception side.
[0155] In addition, the frequency mixer 22 on the reception side
can also employ a harmonic mixer and an even harmonic mixer.
Moreover, almost similar effects can be obtained by operating the
frequency mixer 82 as the two-terminal mixer described in
connection with the first embodiment in the intermediate frequency
band without using the branching filter 74, inputting the second
intermediate frequency multiplex signal wave (frequency: fIFmp2) as
it is and detecting the intermediate frequency signal wave
(frequency: fIF2) in the second intermediate frequency multiplex
signal wave (frequency: fIFmp2) by the reference signal wave
(frequency: fLO4). This is because the fIFmp2 component generated
through the linear detection by the first frequency converting
section 76 has a high power level and enables operation in the
linear detection region. Moreover, by employing a microwave
transistor for the two-terminal mixer, the gain of the microwave
transistor can be positively utilized since the operation frequency
is in a frequency band lower than fIFmp2 (once
frequency-downconverted in the first frequency converting section
76), and higher conversion efficiency from fIF2 to fIF1 can be
obtained.
[0156] In the present embodiment, it is acceptable to insert an
amplifier between the first frequency converting section 76 and the
second frequency converting section 75 in order to adjust the input
level to the second frequency converting section 75 to an
appropriate level (operation region of linear detection) at
need.
* * * * *